For many electronic warfare applications, phased array antennas are used for beam forming or direction finding purposes in which an aircraft, for instance, is provided with an antenna array, the outputs of the elements of which are coaxially cabled to an equipment bay on the aircraft where the signals are processed through a number of different receiver modules. These modules include low noise amplifiers, analog-to-digital converters, filters, mixers, IF stages, amplifiers and processors that constitute a centralized receiver system that is complex, heavy, consumes an excessive amount of power and is expensive.
In addition to weighing in excess of 60 pounds, the input/output (I/O) drivers of such a modular system can consume as much as 15 watts of power out of a 25-watt total, with the power drain primarily residing in the interfaces between the modules. This is because the interfaces must employ drivers that consume an excessive amount of power. Moreover, cabling between the modules and to antenna elements is heavy and leads to cable losses that result in power drain and decreased receiver sensitivity.
Power consumption and weight are indeed factors when one seeks to provide an unmanned aerial vehicle (UAV) such as the Predator with electronic warfare (EW) receiver capabilities. It will be appreciated that unmanned vehicles have limited fuel supplies, or if powered by solar cells, can only accommodate equipment having very limited power consumption. When the UAVs hover over an area sometimes for days, weeks or months, the longevity of the mission is critically dependent upon fuel consumption, which is in turn directly related to power consumption of the avionics package. Moreover, the ability to reduce the weight from the 60-pound modular system described above is critical because weight reduction translates to increased endurance. Size reduction is also a factor because present rack-mounted modular EW systems occupy too much space to be incorporated into the UAV avionics package.
It will thus be appreciated that in high-altitude, long-endurance UAVs the physical size of the avionics package is a problem. Not only does power consumption translate into endurance, but the ability to do the signal processing associated with the EW receivers must be done in packages that are to be located on a platform that is ten times smaller than, for instance the P3 reconnaissance aircraft.
In short, if one were to be able to completely eliminate the modules and the extensive coaxial cabling between modules, one could significantly reduce size, weight and power consumption, while at the same time reducing impedance mismatches that reduce sensitivity.
While one might be inclined to produce an EW receiver using multi-chip modules or MCM technology, it will be appreciated that the multi-chip module approach also consumes a significant amount of power. While the multi-chip module can shrink the size of the system to a certain extent, one must address the I/O interface power requirements, which as mentioned above can result in 15 watts wasted power out of the 25-watt total requirement. Thus, for instance, if one were to make a modular receiver system having, for instance, one module that includes an analog-to-digital converter and a demultiplexer, a second module that contains a low band pass filter, a high band converter, clock and local oscillator generation, a digital automatic gain control coupled to an analog-to-digital converter and another demultiplexer, all of which are coupled to a CMOS DSP processor, which is in turn coupled to a serializer, one would expend 5 watts of I/O power associated with the first analog-to-digital converter. This power consumption is added to a 2-watt current consumption for the I/O to the CMOS digital DSP. Next, there is a loss of 4 watts of power for the output due to the I/O associated with the demultiplexer that is associated with the low band and high band converters, with another 2 watts associated with the I/O to the CMOS DSP. Between the DSP and the serializer, there is another 2 watts of lost power due to the I/O drivers, with another 1 watt of lost power associated with the demultiplexer ahead of the serializer.
While power consumption of a modular receiver utilizing MCM technology is indeed a problem, there is also a requirement to improve on all of the characteristics of an MCM system to not only decrease power consumption for increasing endurance, but also to increase the dynamic range, provide improved instantaneous bandwidth, increase the operating frequency bandwidth beyond the usual 2 GHz to 18 GHz bandwidth, and increase the mean time before failure (MTFB). Note further that one needs to be able to decrease the equipment size from the present size of 200 cubic inches down to something considerably more manageable.